Paleomagnetic Study of Colider Paleoproterozoic Suite and Associated Mafics, Southwestern Amazonian Craton / Estudo Paleomagnético da Suíte Paleoproterozóica Colíder e Máficas Associadas, Sudoeste do Cráton Amazônico

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

This work presents a paleomagnetic study perfomed on felsic volcanic rocks of the Colider Suite (5 oriented cores and 42 oriented hand samples, 12 sites), Flor da Serra and Guadalupe mafic rocks (75 oriented cores and 3 oriented hand samples, 11 sites). These units are situated in the northern Mato Grosso State (southwestern Amazonian Craton), close to the Alta Floresta, Colider, Terra Nova, and Matupá cities. The Colider Suite rocks have been dated by the U-Pb (zircon) method, and ages vary between 1.80 and 1.78 Ga. Radiometric determinations are not yet available for the Guadalupe Intrusive. Two very stable magnetization components were isolated after AF and thermal demagnetization: northern (southern) directions with moderate to steep downward (upward) inclinations (component B - Dm=187.4°, Im=50.9°, N=16, ?95=11.3°, K=11.7) were isolated for most Colider Suite rocks and associated mafic rocks. Northern upward direction with moderate inclination (component A - Dm=356.5°, Im=47.6°, N=3, ?95=15.8°, K=61.9) was found for the Guadalupe gabbro and other two mafic dikes. Rock magnetism experiments show that the magnetization is carried by hematite, which is probably primary in origin, in the felsic rocks. In the mafic rocks the main magnetic carrier is Ti-poor titanomagnetite in the PSD magnetic structure. Two paleomagnetic poles were determined for these components, which are located at 289.4°E, -65.4°N (?95=12.9°) (SC pole, Colider Suite) and 298.8°E, 50.4°N (?95=15.1°) (IG pole, Guadalupe Intrusive). An age of 1.780 ± 7 Ma is attributted to pole SC (quality factor Q=5), which is considered a key pole for the Amazon Craton. Paleogeographic reconstructions using Paleoproterozoic key poles suggest that Laurentia, Baltica, North China and the Amazon Craton were located in laterally contiguous positions forming a huge continental mass (Columbia Supercontinent) at 1830-1770 Ma ago. This hypothesis is reinforced by the geological evidence that paleoproterozoic mobile belts of these four continental masses fit well in the reconstruction, being formed by contemporaneous subduction-related magmatic arc belts with the same tectonic polarity.

ASSUNTO(S)

colider suite suíte colíder paleomagnetic cráton amazônico paleoproterozóico amazonian craton paleoproterozoic paleomagnetismo

ACESSO AO ARTIGO

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